1. Field of the Invention
The present invention relates to a sheet material information detection apparatus for detecting information on a sheet material by applying an external force to a sheet material by using an external force application member driven by electric power, and more particularly, to a control in a case where a power down (a supplication amount of the electric power is lowered or stopped) occurs.
2. Description of the Related Art
In recent years, in a technical field of sheet material processing apparatuses, notably image forming apparatuses (such as Laser Beam Printer, copying machine, and ink jet printer), there is diversification of types of sheet materials to be processed. There is also diversification of users and use environment of the sheet material processing apparatus. Only with regard to the image forming apparatus, for the sheet materials of the diversified types, there is an increase in demand for higher quality (higher image quality, higher processing speed) On the other hand, with the diversification of sheet materials and diversification of processing contents, the number of items to be set by the user becomes enormous, thereby making it difficult to set an optimum processing condition. Therefore, a technique, in which various sensors are arranged in the sheet material processing apparatus to automatically identify sheet material information including a size, a thickness, and a quality of the sheet material, and automatically set an optimum processing condition, is put into practical use in some cases.
Japanese Patent Application Laid-Open No. 2004-038983 discloses a system which makes a database of various pieces of sheet material information including texture, glossiness, absorbency of ink, luminance, gross, color reflection, color depth, graininess, whiteness, humidity, heat loss, adhesiveness, and bonding property, for allowing the database to be shared among a plurality of printers. When a sheet material is designated through a setting screen, a requisite piece of sheet material information is taken out from the database to a selected printer. A processing condition optimized based on the sheet material information is automatically set for the printer.
However, even regarding the same kind of sheet material (paper), the sheet material information including a bending modulus and attenuation characteristics of the sheet material widely changes according to temperature, humidity, storage environment, storage time and the like. A database according to Japanese Patent Application Laid-Open No. 2004-038983 handles a fixed value, so it is difficult to comply with a setting regarding fine differences in an environmental condition mentioned above.
In this case, there is proposed that the sheet material information detection apparatus is incorporated in the sheet material processing apparatus, requisite sheet material information is obtained for each sheet material to be processed, and the sheet material information is fed back to a transport condition and processing condition.
Japanese Patent Application Laid-Open No. 2002-310866 discloses a sheet material information detection apparatus having a structure in which, while a sheet material is sandwiched between an impact transmitting block and a piezoelectric element, an external force application member is dropped by gravity, and an impact force transferred to a support member is detected by the piezoelectric element. In this case, compression characteristics of the sheet material are measured as the sheet material information.
However, the sheet material information detection apparatus as disclosed in Japanese Patent Application Laid-Open No. 2002-310866 cannot detect the bending modulus of the sheet material required for setting the transport condition. Further, the heavy external force application member is dropped from a substantially high position in order to compress a large area of the sheet material, so the sheet material information detection apparatus cannot be mounted on a practical sheet material processing apparatus in which the sheet material information detection apparatus is required to be operated at high frequency in a short period of time.
Japanese Patent Application Laid-Open No. 2005-024550 discloses a sheet material information detection apparatus in which an external force application member is allowed to impact a sheet material and an impact force transmitted to an external force receiving member through an intermediation of the sheet material is detected by a piezoelectric element. In this case, a peak value of a voltage output of the piezoelectric element which is deformed is determined, and a bending modulus of the sheet material is output as sheet material information.
Further, in the sheet material information detection apparatus as disclosed in Japanese Patent Application Laid-Open No. 2005-024550, a gram level of the external force application member is allowed to impact the sheet material with travel of a millimeter level, so the sheet material information having practical accuracy can be detected in a short period of time with high frequency.
In the sheet material information detection apparatus as disclosed in Japanese Patent Application Laid-Open No. 2005-024550, through a transport path which is small in width, that is, a gap between the external force application member and the external force receiving member which are opposed to each other and are assembled to be light weight with high accuracy, the sheet material passes at high speed. Accordingly, in a case where the bent or curled sheet material passes therethrough, or where the sheet materials are sent while being overlapped each other (double feeding), the sheet material impact a wall surface of the transport path, the external force application member, or the external force receiving member at high speed, or clogging (also referred to as jam) of the sheet material may be caused. As a result, the external force application member and the external force receiving member may not stay in adjustment in some cases.
Further, in the sheet material information detection apparatus as disclosed in Japanese Patent Application Laid-Open No. 2005-024550, in order to set a height of the sheet material at which the external force application member is allowed to impact the sheet material, a retaining unit for retaining the sheet material in a thickness direction may be provided.
In this case also, there is a possibility of the sheet material impacting a narrow retaining gap of the retaining unit at high speed, or the sheet material clogging.
In this case, there is conceived a retraction control in which the impact and clogging of the sheet material are electrically detected, and the gap between the external force application member and the external force receiving member opposed to each other and the retaining gap are forcibly widened by using a motor or a solenoid.
However, the retraction control depending on electrical detection, electrical control, and electrical driving, exerts a function thereof in a normal time (at a time when electric power is supplied) However, when the electric power is stopped, the gap between the external force application member and the external force receiving member opposed to each other and the retaining gap are not widened. In a case where the moving sheet material is plunged into the gaps which are not widened, there is a risk in that new clogging (jam) or double feeding of the sheet material, and further, damage of sensors or the like may be caused.
Further, in a case where the clogging or double feeding of the sheet material is caused in a position other than the position of the sheet material information detection apparatus, the electrical detection is not performed. Therefore, the gap between the external force application member and the external force receiving member opposed to each other and the retaining gap are not forcibly widened. In a case where, while the sheet material is left in the gaps remaining narrow, a sheet processing apparatus is turned off and the sheet material is forcibly pulled out for recovery, there is a risk of the sheet material which is restrained in the narrow gaps being ripped. On the other hand, when the sheet material is not ripped, the external force application member and the external force receiving member are strained when the sheet material is pulled out, so the external force application member and the external force receiving member do not stay in adjustment.